Numerous circuits used in radio (high) frequency (RF) electrical devices, such as low noise amplifiers (LNAs), mixers, synthesizers, resistance capacitance (RC) filters and transconductance capacitance (gm-C) filters, require calibration. Specifically, calibration of open loop gain for such circuits is needed, because of the inability at high frequencies to use feedback techniques that normally work in conjunction with readily available matched passive components to set the gain. Gain is thus usually set by matching active transistor components to passive elements such as inductors, resistors and capacitors. Active components on an integrated circuit (IC) do not typically match very well to the passive components. As a result, a method of calibrating the gain to ensure that a design is manufacturable is needed.
Accordingly, separate control circuitry, namely calibration circuitry, is used to provide calibration of the gain of these RF components. Such calibration circuits typically include circuitry similar to or matched to that within the target circuit so that the target circuit may be calibrated for power supply variations, temperature variations, integrated circuit process parameter variations, parasitic capacitance, transconductance and the like. Such calibration circuits typically use the large signal characteristics of the devices in the target circuit. However, such calibration circuits can suffer from inaccuracies due to poor matching of large signal parameters to the small signal parameters, and it is the small signal parameters that determine the gain of the devices. As process geometries get finer, the large signal models for the devices no longer match simple textbook models for the transistors. This makes the task of building these circuits harder. As a result, a method for directly measuring and calibrating the small-signal parameters of transistors is increasingly necessary.